1. Field of Invention
The present invention relates to a photo driver circuit with power saving function, in particular to such a circuit applied to applications in which power consumption is a concern. The present invention also relates to a photo driving method.
2. Description of Related Art
A photo resistor senses the intensity of ambient light and converts it into an electronic signal. Photo resistors are widely used in applications such as night lamps and automobile headlights whose operation is controlled according to the intensity of ambient light. However, photo resistors are not the most satisfactory choice in such electric products because they contain toxic material (metal sulfide), and their response to light is relatively slow.
On the other hand, CMOS photo sensor devices (including photo diodes, photo transistors and photo ICs) are also capable of sensing the intensity of ambient light, while they are non-toxic.
Regardless whether photo resistors or CMOS photo sensor devices are used, they generate larger current when the intensity of ambient light is high; thus a troublesome problem occurs when such devices are applied to illumination control. Taking the night lamp as an example, when the intensity of ambient light is high and the night lamp does not need to function, the circuit consumes large power due to high current generated in the circuit. In this regard, power-saving function is very much desired, in particular when the product is operated by the power of a battery, or in an application wherein power consumption is a concern.
In view of the foregoing, it is desirous, and thus an objective of the present invention, to provide a photo driver circuit with power saving function which can be applied to e.g., Christmas light strings, bicycle headlight, etc.